1. Field of Invention
This invention relates generally to microwave motion sensors and more particularly to microwave sensors implemented using a random pulse generator.
2. Description of Related Art
Typically, microwave sensors are used to detect the presence of moving objects, indicating an intrusion, in an area by sending microwaves to a region that is to be monitored. The microwave sensor transmits a microwave signal toward a region and in the event that movement is detected, the microwave signal is reflected back (echo). The reflected signal is modulated due to the Doppler Effect and is shifted in frequency. The frequency shift is directly proportional to the object's velocity relative to the sensor. Typically, a maximum frequency shift occurs when the target is moving straight towards the sensor and a minimum frequency shift is observed when the object is moving at 90 degrees to the object.
Currently microwave motion sensors are operated with fixed pulse periods. If two sensors are the same kind and are in close proximity to each other, they will eventually interfere with each other, in that the pulse width of each sensor will overlap each other. The overlap may occur due to component tolerances. The resultant overlapped pulse width may cause the microwave sensors to become noisy and create false alarms. Such a condition typically occurs when two or more sensors are installed too close to each other, installed facing each other and when the microwave frequency of the sensors are the same or close to each other.
One method by which the above-mentioned problem can be overcome is to set the sensors at different microwave frequencies. This requires the installer to carry many sensors at different frequencies. However, this practice increases the cost of operation for both manufacturer and the customer, and is not desirable.
Therefore, what is needed is a robust, reliable and cost effective microwave sensor that can be configured to prevent the pulse width from overlapping when the sensors are installed facing each other or close to each other, even if they are set at the same frequency.